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I I I I I I I I I I I I I I I I I I I Geotechnical Engineering Irrvestigation This response infers that the critical abutment seepage is occurring between the dam crest and elevation 10,260, i.e.: a depth ofJO feet below the crest. This does not presume that there is no seepage below reservoir elevation 10,260 feet, only the seep areas, below this reservoir elevation daylight at the toe of the dam or in the downstream rock buttress. Additional water inflow is being contributed laterally (parallel and / or inclined to the embankment axis) from fractures in the abutment rocks. Spring activities are present downstream of the embankment along the extension of the left abutment and the downstream channel slopes. Based on these observations, it is likely that groundwater fonns some component of the observed seepage occurring along the left abutment. The contribution of groundwater inflow is expected to peak during snow melting season which corresponds to maximum storage in the reservoir, when seepage from the reservoir also reaches a peak. B. Evaluation of Seepage Our evaluation of the seepage conditions attributes most of the seepage to migration through the highly fractured abutment rocks. The orientation of the fractures along the rock outcrops observed during our field investigation make this process likely. The point of entry, identified by Hydro-Triad during a dye test, was plotted on the site plan. This point is aligned with the abutment-embankment groin, away from the core contact. Because of the fractured nature of the abutment rock at high elevations, seepage occurs around the end of the core contact with the abutment and re-enters the downstream shell of the dam. Seepage appears at the toe of the downstream section and rises to elevation 10,247 as the reservoir rises. With reservoir lowering the seeps dry up in the reverse sequence. The latest episode indicated that the core saturation rises only slightly and diminishes slowly as well. These responses tend to confinn that saturation is being strongly influenced by seepage from the abutments and there is in general satisfactory integrity of the core. This conclusion is supported by the fact that the water elevation in CE-I was lower, at elevation 10,237 feet, than the seep areas, 10,247 to 10,250 feet elevation. However the response ofCE-2, during grouting, indicates the possibility that some flow could be occurring between CE-2 and CA-!. The soils encountered in that area, B-1, appear to be sandy silt and silty sand, which would not act as an effective barrier against water flow, like a clayey soil would. While the threshold elevation for increased seepage appears to be at about elevation 10,260 feet, it is likely that seepage is occurring at lower levels. However, at these lower reservoir elevations the exit point is at the toe of the embankment, inside the rock buttress or behind the concrete headwall, which poses no stability problems for the dam. Continental Dam Page 5